1. Technical Field
The present invention relates generally to cellular wireless communication networks; and more particularly to the servicing of high data rate packetized data communications within such cellular wireless communication networks.
2. Related Art
Wireless networks are well known. Cellular wireless networks support wireless communication services in many populated areas of the world. While cellular wireless networks were initially constructed to service circuit-switched voice communications, they are now called upon to support packet-switched data communications as well.
The transmission of packetized data communications within a wireless network places different demands on networks than does the transmission of voice communications. Voice communications require a sustained bandwidth with minimum signal-to-noise ratio (SNR) and continuity requirements. Data communications, on the other hand, typically are latency tolerant but have higher total throughput requirements. Conventional circuit-switched wireless networks were designed to support the well-known voice communication requirements. Thus, wireless networks (as well as conventional circuit switched telephone networks) have been adapted to service data communications, with such adaptation providing mixed results. Thus, future wired and wireless networks will likely be fully packet switched.
Because packet data transmissions typically employ a greater bandwidth on the forward link than they do on the reverse link, various standards have been promulgated which focus on high data rate forward link transmissions. These standards include, for example, the high speed downlink packet access (HSDPA) standard. The HSDPA is a backward compatible standard that is compatible with the UMTS standard, which is widely used in Europe. The 1x EV-DO and 1x EV-DV standards will also provide high data rate forward link transmissions. 1x EV-DV will be backward compatible with the 1x RTT standard, which is a member of cdma2000 family of standards. Note that the HSDPA and 1x EV standards typically employ a semi-distributed network architecture.
With the standardization of wireless communications to support high data rate data, various types of high data rate data transmissions will now be possible, e.g., streaming video, streaming audio, and other high data rate transmissions in addition to facilitating packet data transmissions at high data rates. However, during transitory portions of call servicing, the high data rate transmission will be interrupted, and in some cases terminated. For example, when a mobile station that is being serviced by a first base station is handed over to a second base station, provisions must be taken to ensure that little or no lost data or delay in transmission results.
Further, when a mobile station is handed over from a first wireless network to a second wireless network, no data loss, and little interruption in data delivery should occur. However, continued servicing of a data communication during handover with little delay and with no lost data is an extremely difficult task. These difficulties are partially caused because data transmission paths are altered during the handover and because the participating systems oftentimes support different operations, e.g., different physical layers.
Thus, there is a need in the art for a cellular wireless network a methodology for supporting high data rate forward link transmissions when a mobile station is handed over from a first cellular wireless network to a second cellular wireless network.
In order to overcome these shortcomings, among others, the present invention includes structure and operations for minimizing data loss and minimizing delay in data delivery when a mobile station is handed over from a first cellular wireless network (system A) to a second wireless network (system B). Such benefits are accomplished by system A and system B sharing resources during and after the mobile station is handed over from system A to system B.
According to the present invention, both system A and system B support high data rate forward link transmissions to the mobile station. The data communication being serviced before, during, and after system handover is a high data rate data communication, e.g., a data communication established between a data streaming or voice over IP server coupled to the Internet and the mobile station. With the structures and methods of the present invention employed, system A and system B operate in cooperation with one another to provide a substantially seamless handover operation.
When the data communication is initially setup by system A, system A provisions and enables resources to receive data from the Internet intended for the mobile station and to pass the data to the mobile station via a combination of wired and wireless links. In one embodiment, system A services this data communication via a path that includes a Packet Data Serving Node (PDSN) that couples to the Internet, a Base Station Controller (BSC) that couples to the PDSN, and a base station that couples to the BSC and that includes a Base station Transceiving Subsystem (BTS) that services the wireless link to the mobile station. In the embodiment, the PDSN supports IP/PPP protocol layers (layers 4,3), the BSC supports a portion of the Link Layer (D-RLP, layer 2), and the BTS supports a portion of the Link Layer (C-RLP), a MAC layer, and a physical layer. The BSC of system A also performs all layer 2/3 call control functions for the data communication. Further, the link layer serviced by the BSC includes an RLP transmit buffer. System B may include the same, or similar structure.
According to prior art operations, during a system A to system B handover, all components of system A service the data communication until the handover is complete and then are no longer employed to service the data communication. In this prior art operation, therefore, system B would perform all functions previously performed by system A after the handover is completed. During this prior art handover, all transmit data buffer contents are lost during the handover. Because this data delay/loss occurs, data recovery operations are initiated. Not only do these prior art operations disrupt the data and interactive multimedia communication such as VoIP but also, because of the delay introduced, higher level protocols supporting the data communication may terminate the data communication by assuming that the supporting communication links had failed.
Thus, according to the present invention, system A and system B interact to share resources, with such resource sharing reducing delay or disruption in the data communication. According to one aspect of the present invention, layer 2/3 call control functions are anchored in the BSC of system A, even after the data communication, and all data paths associated therewith are handed over from system A to system B. According to another aspect of the present invention, the RLP layer (layer 2) supporting the data communication is anchored in the BSC of system A servicing the data communication. In this case, the BSC of system A interfaces with a serving BTS of system B to service the ongoing data communication. According to still another aspect of the present invention, the RLP layer (layer 2) is handed over to system B but the RLP layer of system B continues to use the RLP transmit buffer of system A that remains in the servicing BSC of system A.
The present invention may be embodied in operations performed by various components of a cellular wireless network. Further, the present invention may be embodied in these various components themselves. Finally, the present invention may be embodied in a plurality of software instructions executed by various components of the cellular wireless network. These, and other features and advantages of the present invention will become apparent from the following detailed description of the invention made with reference to the accompanying drawings.